A) Field of Invention
The present invention relates to communications testing equipment and more particularly to communication testing equipment which tests the longitudinal balance of telephone equipment.
B) Background of Invention
A telephone line generally contains three separate wires. Two of these wires are referred to as the tip and ring wires and the third wire is usually a grounded wire. The actual signal used in telecommunications is carried on the tip and ring wires with the grounded wire being used as a reference.
In the telephone line, the tip and ring wires are continually twisted around one another. Since the telephone line can extend great distances, it can be subject to many disturbances that can cause interference with the electrical signals carried along those lines. By twisting the two wires around each other, it increases the probability of having any disturbances affect both wires equally. This equal distribution of the interference among the two wires reduces the problems caused by any disturbance.
Twisting the tip and ring wires around each other is one attempt of ensuring that the two wires are electrically balanced. An imbalance between the wires increases the susceptibility of noise pick-up that can disrupt the transmission of the signals. Accordingly, it is important to be able to test the wires to determine whether they are equally affected by any disturbances in the wire or whether the wires are imbalanced. In testing the wires, it is important that the test equipment itself does not contribute to the imbalance measurement.
In the prior art, a telephone line is tested for an imbalance by applying a 1 kHz pulse test signal to both the tip and ring wires. By exciting both the tip and ring wires with the same voltage at the same frequency, the line can be monitored to determine whether an imbalance occurs. If the signal on one wire is different from the signal on the other wire, then an imbalance between the wires exists. This prior art is primarily applicable for voice band application.
In applying a 1 kHz test signal, the balance test will return a single measurement representing the balance level between the two wires. If this measurement is below a predetermined level, then the line can be considered to be electrically balanced. The level is empirically determined and approximates the acceptable tolerances of the telephone line.
This test, however, does not adequately predict the vulnerability of the line to be potentially disturbed by noise disruptions. By using only one measurement and comparing it against an empirically set standard, it gives an inaccurate depiction of the balance of the telephone line because it oversimplifies the range of different types of disturbances that can affect the line. For example, disturbances at higher frequencies will not be measured by this 1 kHz test. In addition, this inaccuracy does not address the situation when a disturbance is intermittent and the magnitude of the disturbance varies throughout the day above the audio range.
A typical voice transmission in a telephone line can have frequencies which range up to 4 kHz. Advances in telecommunications have created the need for transmissions at higher frequencies. For example, an XDSL line can operate in the megahertz range. The conventional method of using a 1 kHz pulse to test for imbalances cannot detect when a disturbance in a line is occurring at such high frequencies. In particular, radio waves which operate at those higher frequency ranges can disturb the high frequency signals sent on the telephone line. In addition, the reach and nature of radio waves can vary during the day which makes radio wave interference to be intermittent.
Therefore, there currently exists a need for a balance test to be able to detect imbalances at high frequencies. There also exists a need for a balance test that reports results that more accurately indicate the telephone line""s vulnerability to disturbances due to imbalances in the line.
The current invention involves a wide band spectral balance test. The test initiates a signal on the tip and ring wires of a telephone line that starts with a low frequency tone and increases the frequency in predetermined intervals up to the higher frequency ranges. The line is monitored for the signals carried on both the tip and ring. The signals on both the tip and ring wires are measured and compared. Measurements and comparisons of those measurements are taken at each frequency level. The results are then plotted on a graph indicating the decibels versus frequency.
In accordance with one embodiment of the invention, a wide band spectral tester comprises a signal generator to create a signal at a set frequency and to cause the created signal to be placed on a first wire and a second wire in a telephone line; and a signal receiver to monitor the first and second wires and compare the signals on the first wire against the signals on the second wire to determine whether the first wire and the second wire are balanced; wherein, the signal placed on the first wire is identical to the signal placed on the second wire and the signal placed on the first and second wires includes signals above 1 kHz.
In accordance with another aspect of this embodiment of the invention, the longitudinal balance tester includes a digital signal processor and a digital to analog converter.
In accordance with another aspect of this embodiment of the invention, the longitudinal balance tester includes a numerically controlled oscillator.
In accordance with another aspect of this embodiment of the invention, the longitudinal balance tester includes a digital signal processor, a differential amplifier and an analog to digital converter.
In accordance with another aspect of this embodiment of the invention, the signal generator places the created signal on a grounded wire in the telephone line.
In accordance with another aspect of this embodiment of the invention, the signal receiver includes balanced test wires to connect to the first and second wires in the telephone line.
In accordance with another aspect of this embodiment of the invention, the first and second wires constitute a twisted pair of wires in the telephone line.
In accordance with another aspect of this embodiment of the invention, the created signal includes frequencies above 10 kilohertz.
In accordance with another aspect of this embodiment of the invention, the created signal includes frequencies above 50 kilohertz.
In accordance with another aspect of this embodiment of the invention, the created signal includes frequencies above 100 kilohertz.
In accordance with another aspect of this embodiment of the invention, the created signal include frequencies above 1 megahertz.
In accordance with yet another embodiment of the invention, a method for testing a telephone line for longitudinal balance is disclosed which comprises the steps of creating a signal at a set frequency; the signal including frequencies in the megahertz range; placing the signal on a first and second wire in a telephone line; monitoring and detecting signals on the first and second wires; and measuring any differences between signals on the first and second wires.
In accordance with another aspect of this embodiment of the invention, the signal includes frequencies above 10 kHz.
In accordance with another aspect of this embodiment of the invention, the signal includes frequencies above 50 kHz.
In accordance with another aspect of this embodiment of the invention, the signal includes frequencies above 100 kilohertz.
In accordance with another aspect of this embodiment of the invention, the signal includes frequencies above 1 megahertz.
In accordance with still another embodiment of the invention, a method for testing a telephone line for longitudinal balance is disclosed that comprises the steps of setting an initial frequency; generating a signal at a frequency; causing the generated signal to be placed on a first and second wires in a telephone line; monitoring signals on the first and second wires; measuring any differences between signals on the first wire and signals on the second wire; recording each measurement of differences for the frequency; increasing the frequency level by a predetermined amount; and repeating the generating, causing, monitoring, measuring, recording and increasing steps until the frequency level reaches a predetermined final frequency level.
In accordance with another aspect of this embodiment of the invention, the method further comprises step of displaying the difference measurements against the frequency in graphical form.
In accordance with another aspect of this embodiment of the invention, the predetermined final frequency level is greater than the initial frequency level by 10 kilohertz.
In accordance with another aspect of this embodiment of the invention, the predetermined final frequency level is greater than the initial frequency level by 100 kHz In accordance with another aspect of this embodiment of the invention, the predetermined final frequency level is greater than the initial frequency level by 1 MHz.
In accordance with another aspect of this embodiment of the invention, the predetermined final frequency level is greater than 10 kHz.
In accordance with another aspect of this embodiment of the invention, the predetermined final frequency level is greater than 100 kHz.
In accordance with another aspect of this embodiment of the invention, the predetermined final frequency level is greater than 1 mHz.
In accordance with still another embodiment of the invention, a method for testing a telephone line for longitudinal balance is disclosed that comprises the steps of setting a frequency range to be tested; generating a test signal; said signal including a plurality of frequencies; causing said generated signal to be placed on first and second wires in a telephone line; monitoring signals on said first and second wires; measuring any differences between signals on said first wire and signals on said second wire; recording each measurement of difference for each said frequency that was included in said signal; changing the frequencies that are included in said signal; repeating said generating, causing, monitoring, measuring, recording and changing steps until each frequency in said frequency range has been included in said test signal.